This is not a habitat that most people would associate with mosses and liverworts but the calcareous shell-sand systems that are scattered round our windy coasts have a rich and varied bryophyte flora with a number of rare and threatened species. The most interesting species occur where the sand is irrigated by fresh water, either in dune slacks or where small burns run through the dunes. However, the sand also needs to be mobile enough to prevent the establishment of a complete sward of flowering plants. There are a number of very rare Bryum species which are limited to this habitat in Britain. Bryum species are not the easiest of mosses to identify but two species, Blunt bryum Bryum calophyllum and Baltic bryum Bryum marratii are more straightforward as they have characteristically blunt leaves and distinctive capsules. Both have much of their UK population in Scotland. Petalwort Petalophyllum ralfsii, a pretty little liverwort which is protected under European legislation, also occurs in this habitat at one site in Wester Ross, where there is a large population.
In the north, a number of plants of montane flushes also occur at sea level on the damp shell-sand and these include distinctive mosses such as Short-Tooth hump-moss Amblyodon dealbatus and Down-looking moss Catascopium nigritum, together with the liverworts Irish ruffwort Moerckia hibernica and the nationally rare Gilman’s notchwort Leiocolea gilmannii.
All of these small plants, which exploit gaps in taller vegetation, have big swings in population size from year to year as their dynamic habitat changes. This poses some problems for conservation as it is very difficult to decide if a dramatic decline in a population is part of the natural cycle or something to get really worried about. More generally, this is a habitat which has declined rapidly through the 20th century because of conversion to golf links and afforestation, increasingly intensive agriculture and development for industry and tourism. Most of the best sites are in more remote places such as Invernaver, Sandwood Bay, Islay or the Outer Isles. A few of these species sill retain a precarious hold on the links near Edinburgh. It is here on the east coast that most sites have been lost, to golf links in East Lothian and Fife, to scrub encroachment at Tentsmuir, to forestry at Culbin and to industrial development in Caithness.